DE3005478A1 - OPTICAL DEVICE FOR COPYING PLANE OBJECTS - Google Patents

Description

PAT H N T Λ NI WA > -Τ

D S MDNCHEN 22, THIERSCHSTRASSE 27

TELEGRAMS: MAYPATENT MUNICH

TELEX 52 4487 PATOP

TELEPHONE COS93 223Ο51

T-23-P-1/1677 Munich, I4. February 19

50 232 / MAU Dr M / mw

THOMSON-CSF in F-75088 Paris / France

Optical device for copying flat objects

The invention relates to the field of duplicating extensive planar objects and, more particularly, to an optical device for Copying flat objects on a 1: 1 scale, especially for duplicating masks with high resolution.

By generating a wavefront that is conjugate with a wavefront of the object, one can obtain a real image of the Create object. This generation can be obtained through holography. Starting from that in a holographic carrier recorded hologram of an object and by exposing the hologram to a reading beam, an image of the object exposed during recording. If the reading beam has a direction of propagation which is that of the E reference beam is opposite in the reconstruction, arises a real image of the object, and this image can be placed on a photosensitive support arranged in an image plane to be recorded. Since the rays are coherent, the reconstructed wavefront is stigmatic for all points in the image. However, precisely because of the coherent nature of the recording beams, of the object beam and reference beam, the reconstructed image influenced by laser spots (speckle), which significantly reduce the signal to noise ratio in the restored image. In fact, the picture appears through Blurred points of light, this modulation of the image being superimposed on the image of the surface. For an application which the projection of a real image onto a light-sensitive one Surface requires this phenomenon to be taken into account.

Ö30035 / Ö7S2

There are several ways to limit their effects on the restored (reconstructed) image.

A first possibility is to produce a hologram that is large enough to be larger in the projected image Get resolution than they used to record this Image on the photosensitive support is required. When the size of the light spots ("grains") formed is small with regard to the smallest dimension of the recorded motif, the motif is recorded with a mean noise, which corresponds to the intensity averaged over several points of light. However, such a solution is not sufficient for the reproduction of masks of large dimensions with high resolution.

The averaging can also be obtained by placing one next to the other in a conventional holographic carrier, the

and
cannot be erased / can restore an image after development, produces a large number of small holograms. Each hologram then reproduces a complete, real image of the object on the light-sensitive surface, and the superposition of these images, which contain the same information but different noise, results in an averaging of the noise on the surface. However, in order to improve the signal-to-noise ratio in a ratio η,

2, the number of superimposed images must be η, which is a Requires carrier of the holographic recording with very large dimensions with respect to the object to be reproduced.

The invention is now based on the object of creating an optical device for copying flat objects, which the averaging of the noise enables the disadvantage of blurring of the reconstructed image by light point effects (speckle), taking into account, however, the stigmatic qualities of the reconstructed image obtained by using coherent light are preserved, are preserved.

This object is achieved by an optical device for copying flat objects, with a source for coherent Light, a lighting device that converts the coherent light emitted by the light source into an object wave for illuminating the object and forms a reference wave, and

030035/0752

a photosensitive support, which according to the invention thereby is characterized in that it also comprises an active optical device which detects the object wave emerging from the object and receives the reference wave and, in real time, a conjugate with the incident object wave and applied to the photosensitive Carrier-directed wave restores to form a real image of the object to be copied there, the Lighting device is designed so that the object is successively illuminated several times until the recording saturation is achieved on the photosensitive carrier in order to produce several images of the object in the photosensitive carrier, which have uncorrelated noise effects to be superimposed.

The illumination of the object can be obtained by painting the object several times with a light spot of limited diameter or by exposing the object in its entirety several times in succession through a rotating diffuser. The optically active medium, which enables the generation of a wave front in real time, which coincides with the emitted from the object Wavefront is conjugated, for example, a reversible holographic material or a non-linear material Mix to be working sodium vapor cell.

The invention is illustrated by the following description of exemplary embodiments which refer to the attached figures relates. Show it:

Fig. 1 schematically shows a first embodiment of the invention Apparatus for copying objects by holographic imaging;

2 shows the cycle of writing - erasing the holographic carrier Recording;

Fig. 3 shows a second embodiment of the copying device, which also works with holographic imaging;

Fig. 4 shows a third embodiment of the copying device, which works with non-linear mixing.

The considerable improvement in the image quality obtained by the device according to the invention for copying flat objects is based on the superposition of a large number of

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Images that have uncorrelated noise effects in the plane of the photosensitive support. It is thus possible to achieve a signal-to-noise ratio of the same order of magnitude as that obtained by a device for copying plane objects using an incoherent imaging system, while maintaining the properties associated with the use of coherent light rays, especially while preserving the stigmatism of the restored wavefront for each point on the object. The device shown in FIG. 1 for copying flat objects has a laser of the argon laser type, which emits a parallel beam in the direction of a semitransparent plate 2. The beam reflected by the semitransparent plate 2 is directed onto a convergence lens 3 which bundles it onto the entry surface of the multimodal optical fiber bundle (light guide) 4. This multimodal fiber optic bundle forwards the object beam which emerges from this bundle and is directed onto a slide object 5. The object beam exposes the slide object in an area of limited diameter with the aid of a surface of a spherical wave. The object wave emerging from the slide object 5 is directed onto a light-sensitive electro-optical crystal 8 of large dimensions. This crystal is polarized by means of two electrodes which are connected to the terminals of a polarization source 9. This photosensitive electro-optical crystal can be a BSO crystal (Bi ₁ pSi O ₂₀ ). Such a carrier enables the real-time registration of phase holograms, and because of its good sensitivity, the build-up time t of the space charge field for a diffraction yield η_ ₅ at saturation is in the order of magnitude of one millisecond for an incident-

- 2

the laser power in the order of magnitude of 100mWcm. the symmetrical characteristic of the diffraction yield of the crystal »} as a function of time is shown in FIG. Such a reversible crystal enables the production of Phase holograms and their reading in real time.

This crystal is illuminated by a reference wave emanating from the partially transparent plate 2, with a lens

$ 30035/0752

-A-

bundles this radiation received by it onto the entrance surface of a monomodal optical fiber 7. The radiation emerging from this fiber bundle is directed onto a lens which forms a plane wave front £ _ which _{is intended to interfere with the wave front JC 0} emerging from the object in the light-sensitive electro-optical crystal 8.

The device also has a plane mirror 11 which is parallel to the reference wavefront Σ-η and serves to reflect back onto the crystal 8 that part of the reference beam which was not absorbed by the crystal 8 during registration. This arrangement enables a read wave front conjugated with the reference wave front to be generated and thus a reconstructed wave front conjugated with the incident object wave front to be generated in real time. The real image formed by this wavefront is separated from the real object with the aid of a partition plate 12. This picture is therefore formed in a picture plane, vjnö. a photosensitive support 13 is arranged in this plane to record this image. A correspondingly oriented polarizer 14 enables the light-sensitive carrier to be isolated from the noise. In fact, the polarization state of the reconstructed light beam during reading is different from that of the registration beam because of the birefringence and the rotatability of the electro-optical crystal, and the reconstructed beam can therefore be separated from the surrounding optical noise.

A mechanical displacement device 15 acts on the _{multimodal optical fiber bundle 4 forming the spherical object wave £ o in} order to displace the end of this fiber bundle in such a way that successively the entirety of the object is illuminated through a spot of limited diameter. The object radiation emerging from the object illuminates the crystal in an area also illuminated by the reference beam. This overlining is repeated many times, namely N times. The photosensitive carrier 13 has a writing time constant T which is very much greater than "C, so that there is a large number N of possible scans before the photosensitive carrier 13 is completely registered

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Reconstruction of the same area is that of the slide object introduced modulation corresponding lighting the same from one reconstruction to the next. Against it is the additional lighting that can be traced back to grain effects, grain size of the mask or grain size of the recording material, different. Because of the sweep, the will be sequentially the object wave illuminating the same zone is modified in the two successive exposures, and the interfering lighting due to diffusion through the grains of the mask is different. So will the reconstructed ray also influenced in various ways by the grain effect of the recording material. The superposition of N was not correlated Noise effects lead to a mean noise at the end of the cycle, which is distributed evenly over the entire image area is. It turns out that the signal-to-noise ratio thus obtained is of the same order of magnitude as that obtained with incoherent optics. The scanning device acts on the light guide either gradually or continuously to move its end in two mutually perpendicular directions XY so that the entire surface of the object is scanned will. If the scanning is carried out step-by-step, the speed of movement can be chosen so that that the instantaneous interference system is recorded to saturation and read in real time before illuminating a new zone so that the contrast between that in the material registered interference fringes reached the maximum.

A special reading arrangement has been described to enable continuous observation of the wavefront diffracted by the crystal, the non-absorbed part of the reference beam being _{reflected back} to the crystal by means of the plane mirror 11 parallel to the reference wavefront Σ Ώ. However, the invention is not limited to this particular reading arrangement, and the reading beam conjugated with the reference beam, which enables the reconstruction of a wavefront conjugated with a complex initial wavefront in real time, can be obtained in other ways, e.g. after division by a den Separating plate dividing reference beam.

030035/0752

The first embodiment of the invention is particularly suitable for copying extended flat objects. In fact, a small area of the object is caused by the object wave lit, and the system dar strips will be throughout The extent of the holographic material is registered, whereby the beam incident on the object can be directed in such a way that that the beam emerging from the object is received in a suitable manner by the recording material.

Fig. 3 shows a second embodiment of the device for copying planar objects, which with holographic image generation works, but in this device the object is lit a total of several times in succession, and it a diffuser device is arranged between the light source and the object between two successive illuminations shifted so that the wavefront emerging from the object is modified and in different ways by the Graininess of the object is affected. Likewise, the registered stripe system is from one registration to the next different, so that the reproduced beam differs from the graininess of the holographic recording material being affected. After a sufficient number of registrations and reconstructions, this becomes possible through the light point effect generated noise averaged over the entirety of the photosensitive support. The device shown in Fig. 3 has like that shown in FIG. 1, a laser source 1 and a partially reflective one Plate 2 on.

The optical lighting device has a lens 16 which forms a spherical wave surface which is directed onto the slide object 5 by means of a mirror 17. A diffuser 18 is arranged directly in front of the object 5. This rotatable diffuser is driven by a motor 19. _{The object wave £ Q} emerging from the object 5 is received by a carrier 8 for reversible holographic registration. As in the device shown in FIG. 1, this carrier can be a BSO crystal which is polarized by means of a polarization source 9. The reference beam is formed by the beam which has passed through the plate 2 and is directed onto the holographic carrier by means of a mirror 20.

030035/0752

A system of lenses β and 10 makes it possible to form a _{plane wave Σ R directed onto the support.} To restore it, as in the previous case, a mirror 11 parallel to the surface E throws back the part of the reference beam not absorbed by the carrier to the carrier. As above, the image generation device has the partially reflective plate 12, the polarizer 14 and the photosensitive carrier 13. In order to obtain the best performance from such a device, the object is illuminated for each position of the diffuser for a time corresponding to the time required for the diffraction strip system to register in the holographic carrier until saturation, the reconstruction being obtained in real time. Then the diffuser is rotated and the same operation is repeated. The number of exposures depends on the recording time constant of the photosensitive carrier.

Fig. 4 shows another embodiment of the device in which the planar object according to a zone of limited diameter which scans the entirety of the object, but in this embodiment, the scan obtained by optical deflection means. Also, another type of device is the reconstruction of a Real image of the object forming wavefront allows provided.

The device has a laser source 1, a partially transparent one Plate 2 and an optical deflection device 21 controlled by a control circuit 22. A lens 23 enables from the beam emerging with a variable direction from the deflection device, an illumination spot with a limited area To form diameter with respect to the surface of the object. The control circuit 22, the deflector 21 and the lens 23 are designed so that the illumination spot is the entirety of the object. The beam emerging from the deflector is in a central position (solid line) and in two extreme positions in the X direction are shown. The scanning must also take place in the Y direction perpendicular to X, so that the entirety of the object is scanned. The device which enables the generation of an image wavefront with

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of the wavefront emerging from the object is conjugated, in this embodiment a cell 24 operating by non-linear mixing. This cell can be a cell containing sodium vapor. Such a cell works as follows: If such a cell has two plane waves in opposite directions that interact in the environment,

which are formed by the radiation reflected from the plate 2 by means of the three mirrors 25, 26 and 27 and form "pump waves" and receive the object wave ΣQ , this cell reconstructs in real time a _{wave conjugated with the object wave E Q} , which is related to the incident wave is reinforced. The generation of the amplified wave is instantaneous; the scanning of the object is continuous. This scanning is repeated several times as in the first embodiment, so that the grain effects in each zone of the photosensitive support are averaged. For this it is necessary that the energy of the reconstructed beam scanning the photosensitive carrier is very small compared to the recording energy of the photosensitive carrier, so that the averaging of the optical noise due to the grain effects is well preserved.

The invention is not limited to the specifically described embodiments of the copier. Particularly the scanning device which has been described with reference to the embodiment of FIG. 4 can be replaced by the one shown in FIG. reproduced embodiment can be replaced and vice versa. In addition, in the device shown in FIG. 3, in which the object is illuminated as a whole, for generating a wavefront that is used to create the image and is conjugate with the wavefront emerging from the object, use a non-linear mixing cell as described in the embodiment of FIG.

Generally speaking, in the device according to the invention any device can be used which enables the generation of a wave in real time that corresponds to an object wave is conjugated and used to produce a real image

03003S / 07S2

a photosensitive support is intended, provided
that their resolution is limited only by diffraction, the device for illuminating the object being designed in such a way that the object is successively illuminated several times until the recording on the photosensitive carrier with saturation is obtained in order to produce several images of the object in the photosensitive carrier to be superimposed with uncorrelated noise components.

030035/0752

PAT K N T A N WA · _Τ

□ B MUNICH 22. THIERSCHSTRASSE 27

TELEGRAMS: MAYPATENT MUNICH

TELEX 52 4487 PATOP

TELEPHONE CO.893 2250 51

T-23-P-1/1677 Munich, February 14, 1980

50 232 / MAU Dr M / W

THOMSON-GSF in F-75088 Paris / France

Optical device for copying flat objects

Brief summary (abstract) of the invention

The invention relates to an optical device for copying at magnification 1 using coherent light, which a significant reduction in the effect of light spots (speckle) allows on the copy.

Its object is a device for copying, a device for illuminating the object, a device for Receiving the object wave and reconstructing in real time a wave conjugate with the object wave to produce one having a real image of the object. The copier also has a photosensitive support which is in the Image plane is arranged. The device for illuminating the object forms on the object to be copied an illumination spot of small dimensions with respect to the object, and the Copying device also has scanning devices, which the object several times completely with the illumination spot scan to print a large number on light-sensitive media overlaying images of the same zone with uncorrelated noise phenomena.

The invention is particularly applicable to high resolution, large surface area copying of masks.

Fig. 1

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Claims (12)

PAT ΚΝΤΛΝ WA _Τ D S MÖNCHEN 22, THIERSCHSTRASSE 27 TELEGRAMS: MAYPATENT MDNCHEN TELEX 52 4487 PATOP TELEFON CO893 22 5Ο51 T-23-P-1/1677 Munich, February 14, 1980 50 232 / MAÜ. Dr.M / mw THOMSON-CSF in F-75088 Paris / France Optical device for copying flat objects Patent claims 1. Optical device for copying flat objects, which a source of coherent light, a lighting device that consists of the coherent light emitted by the source Light forms an object wave for illuminating the object and a reference wave, and a photosensitive substrate has, characterized in that it also has an optically active device (8,24) which is used to receive the from the object exiting object wave and the reference wave and for the reconstruction of a conjugate with the incident object wave Wave serves in real time, the conjugate wave being directed onto the photosensitive carrier (13), there to form a real image of the object to be copied, and the lighting device is designed so that the object is illuminated several times one after the other in such a way that several images of the object in the light-sensitive carrier, which have uncorrelated noise components, superimposed will. 2. Device according to claim 1, characterized in that the optically active device is a carrier (8) for reversible holographic registration, which receives the object wave exiting the object and the reference wave and forms a system of interference fringes therefrom, the reconstructed wave with Using a read wavefront is obtained which is conjugated with the reference wavefront also received from the carrier. 03QÖ35 / O7S2 3. Apparatus according to claim 2, characterized in that the reference wave is a plane wave and the device for forming the read wave has a plane mirror (11) which is parallel to the reference wavefront and which is used during registration reflects the non-absorbed part of the reference wave to the carrier (8). 4. Device according to one of Claims 2 and 3, characterized in that that the support for the holographic registration (8) is a light-sensitive electro-optical crystal and the holograms registered in such a carrier are phase holograms are. 5. Apparatus according to claim 4, characterized in that the crystal (8) is a crystal Bi ₁₂ Si O ₂₀ , which is polarized so that the applied electric field is substantially perpendicular to the central direction of the recorded interference fringes. 6. The device according to claim 1, characterized in that the optically active device is a non-linear environment, that the object wave emerging from the object and two pump waves, which are formed from the reference wave and are in the environment in propagate in opposite directions, receive. 7. Apparatus according to claim 6, characterized in that the non-linear medium is a cell containing sodium vapor (24) is. 8. Device according to one of claims 1 to Ii, characterized in that the lighting device illuminates the object in a limited area with respect to the extent of the object and also has scanning device which act on the object wave and move it so that the entirety of the object is scanned , this scan being reproduced several times. 9. Apparatus according to claim 8, characterized in that the object wave is a spherical wave emitted from a point source that starts from the source for coherent light (1) is formed. 030035/0752 10. Apparatus according to claim 9, characterized in that the object wave emerges from an optical fiber bundle (4), and the scanning by mechanical deflection of the end of the fiber bundle (4) is obtained. 11. The device according to claim 9, characterized in that the lighting device is formed from separate elements and forms an object point source, the scanning device is an optical deflection device (21) which acts on the position of the object point source. 12. Device according to one of claims 1 to 7, characterized in that that the lighting device passes through the whole of the object several times in succession through a diffuser (18) illuminated and the device has means (19), which the diffuser (18) between two successive Rotate lights. 030035/0762